Devices for shaking the control column or “stick” which controls fixed wing aircraft are well known and provide an unmistakable warning of an impending stall. Such devices are typically mounted on the aircraft's control column or “stick” and provide a high amplitude low frequency vibration to signal the pilot of an impending stall. Such signals provide an unmistakable warning to the pilot, which cannot be confused with other warnings and signals typically present in an aircraft cockpit. Control column shakers of various designs are manufactured and sold by Safe Flight Instrument Corporation of White Plains, N.Y., the assignee of the present invention.
The use of a control column shaker in rotary wing aircraft is also known, as evidenced by U.S. Pat. No. 4,115,755 to Cotton. As disclosed therein, an alarm such as a shaking of the collective pitch control lever of a helicopter, is used as an indication that the actual acceleration exceeds the permissible acceleration. As disclosed by Cotton, the structural envelope of the helicopter, as defined by weight, air speed, rotor RPM, air density and collective stick position, is used as an indication of permissible loading of the helicopter rotor. Cotton also teaches the use of a gross measure of the aircraft weight, density of the air, air speed, collective pitch and rotor speed of the aircraft as an indication of a table lookup to determine the maximum permissible aircraft acceleration under such flight conditions, which is then compared against the actual aircraft acceleration to determine when the aircraft is maneuvered close to a loading which exceeds the structural envelope.
A helicopter anti torque limit warning device is disclosed in my U.S. Pat. No. 6,002,349. As disclosed therein, the pilot warning system acts on foot pedals which are operatively connected to the controllable force mechanism, with the pedal movement controlling the amount of force exerted by the controllable force mechanism on the tail boom to control the orientation of the helicopter fuselage about the yaw axis. A position sensing device senses the location of at least one of the foot pedals between its first and second positions, and a warning indicator operatively connected to the position sensing device provides a warning to the pilot when the sensed foot pedal reaches a pre-determined distance from one of the first and second positions. The warning indicator provides a tactile warning to the pilot, such as vibration or shaking of the respective foot pedal to provide an unmistakable warning to the pilot that the foot pedal has reached a pre-determined position near its maximum travel position. By such a warning system, the pilot is provided with a tactile input indicating that the helicopter yaw control system is approaching its maximum counter-rotating torque and that the pilot should take appropriate action.
A helicopter tactile exceedance or over stressed warning system for avoiding “hot starts” and other unsafe operating conditions is disclosed in my co-pending application Ser. No. 10/821,974 filed on Apr. 12, 2004 and assigned to the same assignee as the present invention. The system disclosed therein includes a tactile warning device attached to a control stick. A computer or micro processor and a keyboard for entering a safe temperature profile are also provided as well as a thermocouple for measuring the turbine output temperature. The computer compares the actual temperature versus the safe temperature profile and generates a signal to activate the tactile warning device when the actual temperature falls outside of the safe temperature profile to warn a pilot to abort the start. The tactile warning device is also activated during flight operations when an over stressed condition occurs to thereby warn the pilot to take corrective action. In addition, the tactile warning may be activated at a first frequency as an early warning and then at a second frequency as an indication of imminent danger.
While the aforementioned systems provide warnings under certain conditions, they do not address a particular problem associated with helicopter landings. For example, under various conditions, it can be difficult for a pilot to judge the distance from the ground during the final stages of a landing. To be more specific, it can be difficult to judge the distance from the surface of a body of water, to judge the distance from the ground during night operations and for landing in the desert or in other dusty conditions. Further, the difficulty in judging distance can be particularly difficult during the last 6 to 20 feet of altitude.
Accordingly, it is presently believed that there may be a relatively large commercial market for a tactile warning system for warning a helicopter pilot that the aircraft is at a pre-selected altitude and for aiding the pilot in making soft landings. It is also believed that there should be a relatively large commercial market for such systems which are highly reliable and yet relatively inexpensive to manufacture and install. In addition, the systems in accordance with the present invention are of minimal weight and size, easy to install and service, durable and at the same time provide a clear warning to the pilot that the aircraft is relatively close to the ground. The systems in accordance with a preferred embodiment of the invention also includes a tactile warning device that increases in intensity as the aircraft gets closer to the ground to enable a pilot to routinely make soft landings under adverse conditions.